1. Field of the Invention
The present invention relates to an apparatus and a method for purifying wastewater, and more particularly, to an apparatus and a method for purifying wastewater using a back overflowed sludge, which is constructed in a manner that a barrier is set in an SBR water tank to divide the water tank into a turbulent-flow region and a steady-flow region, and sludge passes over the barrier to overflow from the turbulent-flow region to the steady-flow region, to thereby effectively removing nitrogen and phosphorus contained in wastewater inflowing into the water tank, and reducing the energy and cost of treatment. Moreover, if barriers are inserted in forepart of typical SBR, it can be obtained some effect of the present invention. Consequently, the present invention""s principle that sludge in turbulent flow region is flowed backward into steady-flow region by mixer and aerator in reactor can be easily applied to various wastewater treatment reactors.
2. Background of the Related Art
When microorganisms grow rapidly, generally, nitrogen and phosphorus are essential nutriments for activating and propagating microorganisms. In a case where the nutriments such as nitrogen and phosphorus are excessively contained in waste water, however, self-nutritive substances including the hydrophytes propagate rapidly and bring about eutrophication that further make worse the quality of sewage and/or wastewater. Accordingly, biological wastewater treatment process including A2O process, a modified phostrip method, UCT method, VIP method, DNR process, and SBR process were proposed in order to effectively eliminate the nitrogen and phosphorus excessively contained in wastewater.
In general, nitrogen exists in wastewater in the form of organic nitrogen and ammonia nitrogen. The organic nitrogen and ammonia nitrogen are removed from waste water through nitrification by which the organic nitrogen and ammonia nitrogen are biologically oxidized in an aerobic condition to be changed into NO2 and NO3 and denitrification by which NO2 and NO3 reduced to nitrogen gas in an anoxic state. The biological nitrogen and phosphorus removal is explained below in more detail.
Nitrification:
The nitrification includes a process (1) in which microorganisms hydrolyze organic nitrogen to change it into NH+4-N and this NH+4-N is oxidized to NOxe2x88x922 by nitrosomonas, and a process (2) in which the NO2 is oxidized to NOxe2x88x923 by nitrobactor. The nitrification is represented by the following chemical reaction formulas (1) and (2).
NH4+N+1.50O2xe2x86x92NO2xe2x88x92+H2O+2H+ (Nitrosomonas)xe2x80x83xe2x80x83(1) 
NO2xe2x88x92N+1.50O2xe2x86x92NO3xe2x88x92 (Nitrobactor)xe2x80x83xe2x80x83(2) 
Accordingly, the entire chemical reaction formula of the nitrification can be represented by the following formula (3).
NH4+N+2O2xe2x86x92NO3xe2x88x92+H2O+2H+xe2x80x83xe2x80x83(3) 
Therefore, the ammonia contained in wastewater is eliminated therefrom through the aforementioned nitrification.
Denitrification:
The dentrification is the dissimilatory reduction of NO3 or NO2 to N2 gas. In other words, NOxe2x88x923 or NO2 is the electron accepter used in energy generation. The denitrification is represented by the following chemical reaction formula (two-step process) (4). The first step is conversion of nitrite. This stage is followed by production of nitric oxide, nitrous oxide and nitrogen gas. The last three compounds are gaseous product that can be released to the atmosphere.
NO3xe2x88x92xe2x86x92NO2xe2x88x92xe2x86x92NO xe2x86x92N2xe2x80x83xe2x80x83(4) 
Phosphorous removal:
Under certain aerobic condition, more phosphorous may be taken by microorganism in phosphate state. The phosphorus being in the phosphate state is released from the microorganisms under the anaerobic state. When the microorganisms take up more phosphorous under aerobic condition than is needed, they go to the bottom of a water tank because the large amount of phosphate is stored in their cells. Here, the microorganisms that sank down in the water tank become sludge. Accordingly, when the sludge containing the excess phosphorous, accumulated on the bottom of the water tank is eliminated; the phosphorus contained in wastewater is removed therfrom. Under the anaerobic conditon, certain heterophobic bacterics take up simple organic molecular produced by hydrolysis and fermentation. Because no electron acceptor are available, they sequester the electrons and carbon in insoluble intracellular solid, such as (ploy-hydroxy butyric acid). To do this phospherization, the cell requires an activated chemical form, that is, acetyl concenzyme a (HSCoA). Formation of HSCoA is energy consume step, and energy come from hydrolyzing of Ploy-P, which these microorganism also contain and use as an energy-store material. The hydrolysis of Poly-P in microorganism releases phosphate to environment under anaerobic condition.
Accordingly, the phosphorus contained in wastewater can be easily eliminated therefrom by allowing the microorganisms to excessively take the phosphorus during anaerobic condition. To make the microorganisms take excessive amount of phosphorus, it is required to allow the microorganisms to release lots of phosphate, first of all.
When an electron acceptor NO3, for example, exists in the reactor, during process for phosphate release the microorganisms do not release phosphorus effectively. In this case, the environment of reactor is changed from aerobic condition to anaerobic condition so as to eliminate the phosphorus.
To remove organisms, nitrogen and phosphorus contained in wastewater, a conventional purifying apparatus like A2O process includes multi-stage anaerobic, anoxic and aerobic reaction tanks and a settling basin. However, the conventional purifying apparatus (A2O) has problems that its installation cost is high and installation region is large.
To solve the above stated problems, SBR process was developed to operate organic compound, N and P removal process, settling and drawing process in one reactor. However, SBR cannot effectively eliminate the nitrogen and phosphorous because it uses one reactor due to biological mechanism. Therefore, improved SBR in which sludge is returned to the front of SBR reactor like A2O process are being developed and applied to overcome disadvantage of conventional SBR. But, its structure and device is complex and it is difficult to operate process as compared with conventional SBR because improved SBR require pump and pipe for sludge return. Furthermore, it takes a large amount of cost to maintain and manage the apparatus.
Accordingly, the present invention is directed to an apparatus and method for purifying wastewater that substantially obviates one or more problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide an apparatus and method for purifying wastewater using back overflowed sludge, in which sludge flows backward over barriers set inside a water tank to purify wastewater contained in the water tank.
Another object of the present invention is to provide an apparatus and method for purifying wastewater using back overflowed sludge, in which sludge flows backward over barriers set inside a water tank according to a turbulent flow formed when wastewater and sludge contained in the water tank are mixed by aeroactor or mixer, thereby purifying the wastewater.
Yet another object of the present invention is to provide an apparatus and method for purifying wastewater using back overflowed sludge, in which a barrier is set inside an water tank to divide the water tank into a turbulent-flow region and a steady-flow region according to flow type, and sludge flows backward over the barrier from the turbuient-flow region to the steady-flow region to maintain high MLSS in steady-flow region, thereby further improving condition for nitrogen and phosphorous removal.
To accomplish the objects of the present invention, there is provided a wastewater purifying apparatus using back overflowed sludge, comprising a water tank having an inflow port for accepting wastewater and an outlet port for discharging purified water, and a first barrier for dividing the water tank into a steady-flow region and a turbulent-flow region according to flow type, the first barrier submerged in the wastewater when it is filled in the water tank to a predetermined water level to allow sludge in the turbulent-flow region to flow backward into the steady-flow region.
To accomplish the objects of the invention, there is also provided a wastewater purifying apparatus using back overflowed sludge, comprising a water tank having an inflow port for accepting wastewater and a outlet for discharging purified wastewater; a first barrier for dividing the water tank into a working reaction tank and a main reaction tank according to nitrogen and phosphorous removal mechanism, the working reaction tank including a steady-flow region accepting the wastewater through the inflow port, the main reaction tank forming a turbulent-flow region and drawing purified water through the outlet, the first barrier submerged in the wastewater filled in the water tank; and a second barrier for dividing the working reaction tank into an anaerobic region and a buffering region (anaerobic/anoxic region), the anaerobic region accepting the influent, the buffering region (anaerobic/anoxic region) accepting sludge back flowed over the first barrier from the main reaction tank.
To accomplish the objects of the invention, there is provided a wastewater purifying method using back overflowed sludge, comprising a microorganism selection process of adsorbing organisms by maintaining a high F/M ratio using organisms contained in influent; an anaerobic process of forming an anaerobic condition to release phosphorus; a sludge transferring process of allowing sludge in anaerobic region to flow under second barrier from an anaerobic region into a main reaction tank via an anaerobic/anoxic region with influent waste water; an aerobic process of oxidizing organic nitrogen and NH+4 to NOxe2x88x922 and NOxe2x88x923 using an aerator of the main reaction tank, excessively taking in phosphorous into the cell, and generating turbulent flow by rising bubble; an anoxic process of denitrifying the nitrate generated during the aerobic process to remove the nitrogen; a sludge returning process of allowing sludge raised by turbulent flow to flow backward during the aerobic and anoxic process and a mixing process of mix uniformly sludge and influent in water tank and generating turbulent flow; a first settling process of settling the sludge in the anaerobic/anoxic region; a concentration process of concentrating the settled sludge by force of gravity; a returning/transferring process of transferring the concentrated sludge in buffering region into the anaerobic region; a second settling process of settling the mixed sludge in the main reaction tank; and a drawing process of decanting the cleared wastewater without disturbing the settled sludge.
It is to be understood that both the foregoing general description and the following detailed description of the present invention are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.